Pixel electrode structure for a liquid crystal display with a high aperture ratio

ABSTRACT

A pixel electrode structure for a liquid crystal display with a high aperture ratio increases the aperture ratio and eliminates Mura phenomenon. Any two adjacent pixel electrodes are disconnected to each other. Each pixel electrode comprises a first-lengthwise periphery that overlaps a first-adjacent data line to form a first overlapping portion, and a second-lengthwise periphery that overlaps a second-adjacent data line to form a second overlapping portion. The first-lengthwise periphery and the second-lengthwise periphery have an identical triangle-wave profile and are symmetrical to each other. The triangle-wave profile is formed by connecting a plurality of right-angled and equilateral triangles.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a liquid crystal display (LCD) that has a highaperture ratio (HAR), and more particularly, to a pixel electrodestructure for the LCD with HAR.

2. Description of the Related Art

As resolutions of liquid crystal display (LCD) increase, aperture ratioof the LCD becomes more and more insufficient. Recently, color filter onarray (COA) technology, has been developed to provide a LCD of highaperture ratio. In the HAR process, the color filter process isintegrated with the TFT array process on the same glass substrate, thusthe aperture ratio of the TFT-LCD device is increased to effectivelyimprove brightness of the panel, and the step of attachment/alignmentbetween a color filter substrate and a TFT array substrate is omitted toimprove yield and decrease process costs. Moreover, in the HAR process,an overlapping portion is formed between a transparent pixel electrodeand a data line to decrease the required area of a black matrix (BM)layer, resulting in a higher aperture ratio in the TFT-LCD device.

FIG. 1 is a top view showing an electrode structure in a pixel of aconventional TFT-LCD device formed using a HAR process. FIG.2 is asectional diagram along line I-I of FIG. 1 showing the rotatingorientations of liquid crystal molecules in the conventional TFT-LCDdevice using a HAR process.

The conventional TFT-LCD device comprises a plurality of traversing gatelines 12 and data lines 14 extending lengthwise to define a plurality ofpixels 10 in a matrix, each pixel 10 comprising a pixel electrode 16 anda TFT. Using one data line 14 as the boundary, a first pixel 10A iscovered by a first pixel electrode 16A, and a second pixel 10B iscovered by a second pixel electrode 16B. Also, the periphery of thefirst pixel electrode 16A overlaps one side portion of the data line 14,the periphery of the second pixel electrode 16A overlaps another sideportion of the data line 14, and a predetermined distance is kept tospace the first pixel electrode 16A from the second pixel electrode 16Bover the data line 14. Further, an arrow P indicates alight-polarization planar direction on a polarizer, a light-entrydirection.

During a HAR process on a TFT array glass substrate 17, a first metallayer is patterned as the gate lines 12, and then an insulating layer 15is deposited to cover the gate lines 12 and the glass substrate 17.Next, processes corresponding to TFT are performed on a predeterminedarea of the gate line 12, and a second metal layer is patterned as thedata lines 14. Next, a transparent conductive layer is patterned as thefirst pixel electrode 16A and the second pixel electrode 16B.

In a case using TN-type (twisted nematic type) LCD, when an extravoltage exceeds a critical value, the liquid crystal molecules 18originally parallel to the alignment film are rotated to becomeperpendicular to the alignment layer in accordance with the magnitude ofthe lengthwise electric field. However, a transverse electric field isgenerated between the periphery of the first pixel electrode 16A and theperiphery or the second pixel electrode 16B, thus the inclineddirections of the liquid crystal molecules 18I and 18II near theperiphery of the pixel electrodes 16A and 16B are influenced by thelengthwise and transverse electric field. Also, when an included anglebetween the arrow P (a light-polarization planar direction on apolarizer) and the long-axis direction of the liquid crystal molecule18I is 45°, an ellipsoidal polarized light caused by birefringenceeffect may pass an analyzer perpendicular to the polarizer to result inlight leakage. With regard to the rotating orientation of the liquidcrystal molecules 1811 over the sidewall of the data line 14, however, aMura phenomenon occurs, manifesting as non-uniform color difference, toform a light leakage area L.

In another attempt to solve the above-described problems, the width ofthe data line 14 is increased to shield the light leakage area L, butthis decreases the aperture ratio of the TFT-LCD device.

SUMMARY OF THE INVENTION

Accordingly, an object of the invention is to provide a pixel electrodestructure in an LCD to increase the aperture ratio and eliminate Muraphenomenon near the overlapping portion between the pixel electrode andthe data line.

To achieve these and other aims, the invention provides a pixelelectrode structure of a liquid crystal display with a high apertureratio. A first substrate and a second substrate are disposed parallel toeach other, such that an internal space is formed between the interiorsurface of the first substrate and the interior surface of the secondsubstrate. A liquid crystal layer is formed in the internal space. Atleast one polarizer is formed on the exterior surface of the firstsubstrate or the exterior surface of the substrate. A plurality ofparallel gate lines is transversely formed on the interior surface ofthe first substrate. A plurality of data lines parallel and extendslengthwise on the interior surface of the first substrate. A pluralityof pixels is defined by the gate lines and the data lines in a matrix,in which each pixel comprises at least one TFT formed on the interiorsurface of the first substrate and near the intersection of the gateline and the data line, a common electrode on the interior surface ofthe second substrate, covering the pixel, and a pixel electrode on theinterior surface of the first substrate, covering the pixel.

In one preferred embodiment, no two adjacent pixel electrodes areconnected to each other. Each pixel electrode comprises afirst-lengthwise periphery that overlaps a first-adjacent data line toform a first overlapping portion, and a second-lengthwise periphery thatoverlaps a second-adjacent data line to form a second overlappingportion. The first-lengthwise periphery and the second-lengthwiseperiphery have an identical triangle-wave profile and are symmetrical toeach other. The triangle-wave profile is formed by connecting aplurality of right-angled and equilateral triangles.

In another preferred embodiment, no two adjacent pixel electrodes areconnected to each other. Each pixel electrode comprises afirst-lengthwise periphery that overlaps a first-adjacent data line toform a first overlapping portion, and a second-lengthwise periphery thatoverlaps a second-adjacent data line to form a second overlappingportion. The first-lengthwise periphery and the second-lengthwiseperiphery have an identical square-wave profile, and the square-waveprofile is formed by connecting a square protrusion and a squareindentation in sequence. The square protrusion of the first-lengthwiseperiphery corresponds in position to the square indentation of thesecond-lengthwise periphery, and the square indentation of thefirst-lengthwise periphery corresponds in position to the squareprotrusion of the second-lengthwise periphery.

DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference is madeto a detailed description to be read in conjunction with theaccompanying drawings, in which:

FIG. 1 is a top view showing an electrode structure in a pixel of aconventional TFT-LCD device with high aperture ratio.

FIG. 2 is a sectional diagram along line I-I of FIG. 1 showing therotating orientations of liquid crystal molecules in the conventionalTFT-LCD device with high aperture ratio.

FIG. 3A is a sectional diagram of an electrode structure in a pixel of aTFT-LCD device according to the first embodiment of the presentinvention.

FIGS. 3B and 3C are top views of an electrode structure in a pixel of aTFT-LCD device according to the first embodiment of the presentinvention.

FIG. 4 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the second embodiment of the present invention.

FIG. 5 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the third embodiment of the present invention.

FIG. 6 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION First Embodiment

A first embodiment of the present invention is now described withreference to FIGS. 3A through 3C. FIG. 3A is a sectional diagram of anelectrode structure in a pixel of a TFT-LCD device according to thefirst embodiment of the present invention. FIGS. 3B and 3C are top viewsof an electrode structure in a pixel of a TFT-LCD device according tothe first embodiment of the present invention.

In FIG. 3A, the TFT-LCD device comprises a lower substrate 1 and anupper substrate 2 parallel to each other, and a liquid crystal layer 3in the internal space between the lower substrate 1 and the uppersubstrate 2. A lower polarizer 4 is formed on the exterior surface ofthe lower substrate 1, an upper polarizer 5 is formed on the exteriorsurface of the upper substrate 2, and a common electrode 7 is formed onthe interior surface of the upper substrate 2. An arrow L indicates alight-incident direction, and an arrow P indicates a light-entrydirection (a light-polarization planar direction of the polarizer 4 and5). The included angle between the arrow P and the X axis is 45°.

In FIGS. 3B and 3C, on the interior surface of the lower substrate 1, aplurality of transverse-extending gate lines 22 and a plurality oflengthwise-extending data lines 24 are patterned to define a pluralityof pixels 20 in a matrix. Each of the pixels 20 comprises a pixelelectrode 26 and a TFT 6. Using one data line 24 as the boundary, afirst pixel area 20A is covered by a first pixel electrode 26A, and asecond pixel area 20B is covered by a second pixel electrode 26B. Also,the periphery of the first pixel electrode 26A overlaps one side portionof the data line 24, the periphery of the second pixel electrode 26Aoverlaps another side portion of the data line 24, and a predetermineddistance is kept to space the first pixel electrode 26A from the secondpixel electrode 26B over the data line 24.

The first key feature of the first embodiment is that the periphery ofthe pixel electrode is a triangle-wave profile. Particularly, within oneoverlapping portion between the first pixel electrode 26A and the dataline 24, the periphery of the first pixel electrode 26A is atriangle-wave profile. Similarly, within the other overlapping portionbetween the second pixel electrode 26B and the data line 24, and theperiphery of the second pixel electrode 26B is a triangle-wave profile.

Preferably, in FIG. 3C, the triangle-wave profile is formed byconnecting a plurality of right-angled and equilateral triangles. Forexample, each triangle constitutes a first hypotenuse 27I (upper righttoward lower left), a right angle θ₁, and a second hypotenuse 27II(upper left toward lower right). Thus, the angle θ₁ at the protrudingportion of the triangle-wave profile is 90°, the included angle θ₂between the first hypotenuse 27I and the X axis is 45°, and the includedangle θ₂ between the second hypotenuse 27II and the X axis is 45°. Also,the first hypotenuse 27I of the first pixel electrode 26A is parallel tothe first hypotenuse 27I of the second pixel electrode 26B, and thesecond hypotenuse 27II of the first pixel electrode 26A is parallel tothe second hypotenuse 27II of the second pixel electrode 26B.

The second key feature of the first embodiment is that the overlappingportion between the pixel electrode 26 and the data line 24 is largerthan the total area of the triangles. Preferably, the width of the dataline 24 is about 10 μm.

In a case using TN-type (twisted nematic type) LCD with aparallel-treatment alignment film, when an extra voltage exceeds acritical value, the liquid crystal molecules 28 originally parallel tothe alignment film are rotated to become perpendicular to the alignmentlayer in accordance with the magnitude of the lengthwise electric field.With regard to the rotating orientation of the liquid crystal molecules28I and 28II near the overlapping portion between the data line 24 andthe periphery of the first pixel electrode 26A, a transverse electricfield generated between the periphery of the first pixel electrode 26Aand the periphery of the second pixel electrode 26B is influenced by thetriangle-wave profile so as to incline. For example, an arrow E₁indicates a first-inclined electric field generated between the firsthypotenuse 27I of the first pixel electrode 26A and the first hypotenuse27I of the second pixel electrode 26B. An arrow E₂ indicates asecond-inclined electric field generated between the second hypotenuse27II of the first pixel electrode 26A and the second hypotenuse 27II ofthe second pixel electrode 26B. Therefore, the first liquid crystalmolecule 28I rotates in the direction of the arrow E₁, and the secondliquid crystal molecule 28II rotates in the direction of the arrow E₂.

Concerning the light-polarization planar direction on the polarizershown by the arrow P, an included angle between the arrow P and thelong-axis direction of the first liquid crystal molecule 28I is 90°, andthe long-axis direction of the second liquid crystal molecule 28II isparallel to the arrow P. This avoids birefringence effect, that is, noellipsoidal polarized light passes an analyzer. Thus, Mura phenomenondoes not occur near the boundary of the data line 24, eliminating lightleakage.

The rotating orientations of liquid crystal molecules near theoverlapping portion between the data line 24 and the periphery of thesecond pixel electrode 26B are similar to the above-describedphenomenon, with no need for further description.

Second Embodiment

FIG. 4 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the second embodiment of the present invention. Mostof the electrode structure in the second embodiment is similar to thefirst embodiment, and the identical parts are omitted with no need forfurther description. The difference is that the width of the data line24 is reduced to make the area of the overlapping portion equal to thetotal area of the triangles. This can achieve the same advantages asdescribed in the first embodiment. Also, by reducing the width of thedata line 24 to achieve 3˜10 μm, the aperture ratio of the TFT-LCDdevice is further improved.

Third Embodiment

FIG. 5 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the third embodiment of the present invention. Mostof the electrode structure in the third embodiment is similar to thefirst embodiment, and the identical parts are omitted with no need forfarther description. The difference is that the periphery of the firstpixel electrode 26A is a square-wave profile, and the periphery of thesecond pixel electrode 26B is a square-wave profile. The square-waveprofile is formed by connecting a square protrusion and a squareindentation in sequence. Particularly, the square protrusions of thefirst pixel electrode 26A correspond in position to the squareindentations of the second pixel electrode 26B, and the squareindentations of the first pixel electrode 26A correspond in position tothe square protrusions of the second pixel electrode 26B.

In a case using TN-type (twisted nematic type) LCD with aparallel-treatment alignment film, when an extra voltage exceeds acritical value, the liquid crystal molecules 28 originally parallel tothe alignment film are rotated to become perpendicular to the alignmentlayer in accordance with the magnitude of the lengthwise electric field.With regard to the rotating orientation of the liquid crystal molecules28I and 28II near the overlapping portion between the data line 24 andthe periphery of the first pixel electrode 26A, a transverse electricfield, as shown by an arrow E, is generated between the periphery of thefirst pixel electrode 26A and the periphery of the second pixelelectrode 26B. Therefore, the rotating orientations of the liquidcrystal molecules 28I and 28II are influenced by the transverse electricfield E and the lengthwise electric field.

Concerning a light-polarization planar direction on the polarizer asshown by the arrow P, when an included angle between the arrow P and thelong-axis direction of the liquid crystal molecule 28I or 28II is 45°,an ellipsoidal polarized light caused by birefringence effect may passan analyzer to cause Mura phenomenon, resulting in a first light leakagearea L₁ near the square indentation and a second leakage area L₂ nearthe square protrusion. However, since the data line 24 shields thesecond leakage area L₂, Mura phenomenon is eliminated.

The rotating orientations of liquid crystal molecules over theoverlapping portion between the data line 24 and the periphery of thesecond pixel electrode 26B is similar to the above-described phenomenonwith no need for further description.

Fourth Embodiment

FIG. 6 is a view of an electrode structure in a pixel of a TFT-LCDdevice according to the fourth embodiment of the present invention. Mostof the electrode structure in the fourth embodiment is similar to thefirst embodiment, and the identical parts are omitted with no need forfurther description. The difference is that each sidewall of the dataline 24 is a triangle-wave profile; with the features of thetriangle-wave profile the same as the first pixel electrode 26A and thesecond pixel electrode 26B. Preferably, the triangle-wave profile isformed by connecting a plurality of right-angled and equilateraltriangles. Each triangle constitutes a first hypotenuse 27I (upper righttoward lower left), a right angle, and a second hypotenuse 27II (upperleft toward lower right). Thus, the angle θ₁ at the protruding portionof the triangle-wave profile is 90°, the included angle θ₂ between thefirst hypotenuse 27I and X axis is 45°, and the included angle θ2between the second hypotenuse 27II and X axis is 45°.

Also, the first hypotenuse 27I of the data line 24 is parallel to thefirst hypotenuse 27I of the first pixel electrode 26A and parallel tothe first hypotenuse 27I of the second pixel electrode 26B, and thesecond hypotenuse 27II of the data line 24 is parallel to the secondhypotenuse 27II of the first pixel electrode 26A and parallel to thesecond hypotenuse 27II of the second pixel electrode 26B.

While the invention has been described by way of example and in terms ofthe preferred embodiments, it is to be understood that the invention isnot limited to the disclosed embodiments. To the contrary,, it isintended to cover various modifications and similar arrangements (aswould be apparent to those skilled in the art). Therefore, the scope ofthe appended claims should be accorded the broadest interpretation so asto encompass all such modifications and similar arrangements.

1-14. (canceled)
 15. A liquid crystal display, comprising: a firstsubstrate and a second substrate disposed opposite each other with aliquid crystal layer interposed therebetween; a plurality of pixelsdefined by crossing gate and data lines formed on the first substrate;and a pixel electrode having a first wave-shaped edge portion formedover the first substrate in each pixel, wherein the pixel electrodeoverlaps a portion of the data line to form an overlapping portion;wherein the area of the overlapping portion is equal to or larger thanthe area of the first wave-shaped edge portion.
 16. The liquid crystaldisplay as claimed in claim 15, wherein the first wave-shaped edgeportion has a square-wave profile.
 17. The liquid crystal display asclaimed in claim 16, wherein the square-wave profile is formed byconnecting a square protrusion and a square indentation in sequence. 18.The liquid crystal display as claimed in claim 15, wherein the data linehas a second wave-shaped edge portion.
 19. The liquid crystal display asclaimed in claim 18, wherein the second wave-shaped edge portioncorresponds to the first wave-shaped edge portion.
 20. The liquidcrystal display as claimed in claim 15, further comprising at least onepolarizer disposed on an exterior of the first or second substrate. 21.The liquid crystal display as claimed in claim 20, wherein an includedangle between a light-polarization planar direction of the polarizer andan X axis is 45 degree.
 22. The liquid crystal display as claimed inclaim 15, wherein the liquid crystal layer comprises TN-type liquidcrystal molecules.
 23. A liquid crystal display, comprising: crossinggate and data lines formed on a substrate; and a plurality of pixelelectrodes formed in an area defined by the gate and data lines, whereintwo adjacent pixel electrodes are disconnected to each other; whereineach pixel electrode comprises a first wave-shaped edge portionoverlapped with a portion of the data line; wherein the data line has asecond wave-shaped edge portion; wherein the second wave-shaped edgeportion corresponds to the first wave-shaped edge portion.
 24. Theliquid crystal display as claimed in claim 23, wherein the firstwave-shaped edge portion has a square-wave profile formed by connectinga square protrusion and a square indentation in sequence.
 25. The liquidcrystal display as claimed in claim 23, wherein the first wave-shapededge portions of adjacent pixel electrode are engaged with each other.